Vehicle diagnostic scan tools are used to diagnose issues in the vehicle under test. The scan tools are built with increasing capabilities that include larger color screens that are capable of being read in direct sunlight, and internet and networking capabilities and thus require more power. The tool can be directly linked to a vehicle's data link connector (DLC) in order to communicate with the vehicle's on-board diagnostic system, such as OBD-II (On Board Diagnostic). Once the tool is connected to the DLC, it can draw power from the vehicle's battery. However, depending on the usage, the tool can draw too much power from the vehicle's battery and damage the vehicle's battery. Additionally, the scan tool can be equipped with its own internal power supply (battery), however, by using the scan tool's internal power supply the amount of time that a technician can use the scan tool is limited.
Accordingly, it is desirable to provide a system and method that power balance the scan tool's draw of power between a vehicle, the scan tool's battery and any other available power source.